From Sally's Baking Addiction
Crust:
1/2 c (113g) butter, melted
1/4 c (50g) sugar
1 tsp vanilla extract
1/4 tsp salt
1 c (125g) flour
Filling:
2 large apples, peeled and thinly sliced
2 Tbs flour
1 tsp cinnamon
1/8 tsp nutmeg
Topping:
1/2 c (43g) old-fashioned whole rolled oats
1/3 c (70g) packed light or dark brown sugar
1/4 tsp cinnamon
1/4 c (31g) flour
1/4 c (56g) butter
homemade salted caramel or store-bought caramel sauce
Directions:
Preheat oven to 300F/149C. Grease bottom of 8-in square pan.
Make the crust: stir melted butter, sugar, vanilla and salt in a medium bowl. Add flour and stir until everything is combined. Press into baking pan and bake 15 min. Them remove from oven.
Make the filling: While the crust bakes, combine apples, flour, sugar, cinnamon and nutmeg in a bowl and mix until evenly coated.
Make the topping: whisk oats, brown sugar, cinnamon and flour together in a medium bowl. Cut in the chilled butter until the mixture resembles coarse crumbs.
When the crust has baked for 15 min, turn the oven up to 350F/177C. Layer apples on the crust, then top cover with the topping. Bake for 30-35 min until the streusel topping is golden brown. Remove and cool 20 min., then chill in the fridge at least 2 hours or overnight if time allows. Cut into bars and serve drizzled with caramel sauce. These can be served warm, cold or room temperature.